CA1136844A

CA1136844A - Method of incorporating additives in polymeric materials

Info

Publication number: CA1136844A
Application number: CA000330042A
Authority: CA
Inventors: Chester C. Swasey; Morris Blumberg
Original assignee: Sandoz AG
Current assignee: Sandoz AG
Priority date: 1978-06-19
Filing date: 1979-06-18
Publication date: 1982-12-07
Also published as: NL7904695A; BE877069A; JPS5538867A; GB2025980B; AU4810979A; ES481687A1; FR2432031A1; IT1121836B; US4238384A; GB2025980A; IT7923693A0; DE2924281A1; BR7903839A

Abstract

METHOD OF INCORPORATING ADDITIVES IN POLYMERIC MATERIALS

Abstract of the Disclosure The incorporation of an additive into a thermo-plastic polymer by melt blending can be controlled by in-corporating the additive in the form of a cohesive blend with an indicator substance such as an optical brightener, and checking the distribution of the indicator in the final product, e.g. by fluorescence measurements. The presence of a certain quantity of the indicator in a sample ensures the presence of a quantity of additive corresponding to the ratio of additive to indicator in the cohesive blend.

Description

1~3~4 C~ 650~6~,8 IMPROVEMENTS IN OR RELATING TO ORGANIC COMPOUNDS

This invention relates to a method of incorporating additives in thermoplastic organic polymers.
It is known to disperse additives, such as stabilizers, ~ntioxidants and lubricants, in thermoplastic polymers by melt blending the additives and tile polyrer in suitable equipment for example roll mills, Banb~ry mixers, ribbon blenders or extruders. The additives may be added directly to and mixed with molten polymer or, in a preferred method, the additives and the polymer are first brought together in particulate form, blended in the solid state and then heated to render one or more of the components, normally the polymer, molten for melt blending. It can happen, however, that the rate of feed of the polymer or one or more of the additives is improper or that the extent of mixing in either the solid or molten state is insufficient, with the result that portions of the polymer receive too much or not enouyh additive. Those portions with insufficient additive may not be able to withstand ~he conditions of further processing or the conditions to which they will be subjected in their final fabricated form. Those portions with too much additive may t .

- 2 - 650-6~1~

also be deleteriously affected, as by odour, colour or mechanical weakening.
Because they are normally used in lo~l concentrations it has been difficult to determine whether additives have been uniforMly dispersed or whether a given s~mple of polymer contains the desired concentration of additive. In particular when additives are melt blended with a polymer in a colltinuous process, it has not been possible to continuously monitor the additive concentration in the product. Instead, samples must be removed for chemical analysis, and this requires so much time that it is not practicable to control the process by changing the mixing conditions in response to the analysis results.
For example, in the production of polyolefins, the polyolefin powder formed in the polymerisation eactor may be continuously blended with additives such as stabilizexs and antioxidants in a melt extruder and extruded into pellets which are sold for ~urther fabrication. As continuous control of the process by analysis of the end product has not been feasible, it ~s common practice to add an arbitrary 10~
more additive than the calculated optimum quantity. This generally succeeds in eliminating portions with insufficient additive, which could decompose on further processing, but is wasteful and may give portions having enough excess additive to adversely aflect the polymer propertles.
The present invention provides a process for the ~3~4~

- 3 - 650-6~18 .

production of a thermoplastic organic polymer containing an additive capable of improving its properties, compr.ising the steps of incorporating into the thermoplastic organic polymer a composition comprising a uniform blend of the additive and an indicator substance which gives a detectable response to irradiation, subjecting at least part of the product.

to the irradiation to which said indicator substance is responsive and determining from the degree of response the amount of the additive in that part of the product.

Suitable additives are those which are normally solid at room temperature and include conventional anti-oxidants, heat-sta~ zers.! UV-stabilizers..~ lubricant-s, flameproo~ing agents, slip agents, anti-blocking agents, anti-static agents, etc. For the purposes of the present invention, the particular chemical identity of the additive is not important. I~owever, as will be discussed more fully below, physical characteristics, particularly the melting point, may be significant. Typical examples of suitable additives are listed in the Modern Plastics Encyclopedia, 1~77-1978, pages 655-709. A single additive, or a mixture of any number of different additives may be used. Preferably the additives used include at least one anti-oxidant, more preferably a mixture of an anti-oxidant and a heat-stabilizer.
The indicator substance should be compatible with the additive and the thermoplastic polymer in the sense of not exuding therefrom, should be stable under the processing conditions to which it will be subjected and must not introduce any undesirable characteristics into the polymer , .

~L~3~
~ 4 ~ 650-6818 product. It must also bc detectable,either visually or instrumentally, by its response to irradiation in the presence of the additives with which it is employed, following incorporation in the thermoplastic polymer. The preferred indicator substances are fluorescent substances which absorb ultraviolet light in the range 300 to 420, preferably 350 to 400 nanometers and fluoresce in the range of 400 to 700, preferably 420 to 490 nanometers.
As will be appreciated, some of the additives mentioned above may themselves be fluorescent. However in most instances they do not fluoresce with sufficient intensity to be reliable self-indicators. For example, variations in the degree of crystallinity of the thermoplastic polymer may cause variations in fluorescence which could interfere with the fluorescence of the indicator. Moreover, the presence of other U.V. absorbing additives may also cause errors in inter-pretation. Accordingly, the preferred indicator substances are those which exhibit a high enough fluorescence intensity to overcome any interference by any other U.V. absorbing materials which may be present. Such preferred indicators are those which, at room temperature, have a log fluorescence intensity ~ 3 at a concentration of 1 ppm in a solvent mixture of diethylether, isopentane, ethanol and chloroform in a volume ratio Gf 75:75:30:20. This can be determined by measuring the 1uorescence at the wavelenqtl!s of maximum excitation and emission using an A,ninco-Bo~man spectrofluor--1~3~8g~g~

imeter with a potted RCA IP28 photomultiplier tube and a ~ryans 21000 X-Y recorder, as described by Kirkbright, Narayanaswamy and West, Anal. Chim. Acta. 52 (1970) 237-246.
Compounds which are useful as optical brighteners are particularly suitable as indicators. Such compounds include various 3-phenyl coumarin, stilbene, py azole, polyphenylene, triazole and styrene derivatives as well as numerous other compounds having the conjugated unsaturation which character-izes optical brighteners. Suitable compounds are disclosed in the following U.S. Patents: 2,983,68~; 3,288,801;
3,28~,804; 3, 453,268; 3,485,831; 3,635,959; 3,637,672;
3,682,946; 3,689,425; 3,732,221; 3,784,570; 3,798,231;
3,821,240; 3,880,841; 3,891,632 and 3,940,388, as well as many othe;^s.
While such compounds give high enough fluorescence intensity to overcome interference by U.V. absorbing additives, it will be understood that detection of their fluorescence will not normally be possible where the polymer is strongly coloured by the addition of dyes or pigments.
While fluorescent compounds are preferred as the indicator substance, the process of the invention includes the use of substances giving other measurable responses to irradi~tion, such as infra-red absorption or reflectance.
Enough indicator should be used so that when it is diluted with additive and polymer it will still glve a readily detectable response to irradiation in ~he final product. On 1~3~
- 6 - ~50-G81 the other hclnd, care should be taken to avoid using such excessive amounts as to adversely affect the properties of the final product. Generally, the amount of indicator ~
be in the range 0.001 to 100, preferably 0.01 to 50 parts 5 per million, based on the total weight of polymer in which it is to be ultimately dispersed~ More preferably, the amount used will be in the range 0.05 to 5, especially 0-05 to 2 parts per million.
It is important that the mixture of additive and 10 indicator substance be uniform when it is added to the polymer so that the presence of indicator in a portion of polymer can be relied on to assure the simultaneous presence of additive in the same portion. In order to prevent possible separation of the components during 15 handling or transit, it is preferred to produce the mixture in the form of a uniform cohesive blend, that is, in the form of solid particles, of which each particle comprises a mixture of additive and indicator substance, the distrib-ution of the additive and indicator substance in the cohesive 20 blend being uniform. This may be accomplis}led for example by melt blending the additive and the indicator substance and then converting the molten mass to finely aivided solid particulate rorm. ~xactly how this is achieved will depend on the melting points of the various components. In some 25 instances all of the components may be melted by heating above - the melting point of the highest melting component or above ~136~

_ 7 _ 650-~18 the eutectic melting point. In another procedure the blend of additlve and indicator substance is heated to the temperature at which the component with the highest melting point dissolves in the others. Also, an additive may be 5 melted while the indicator substance remains in solid form and becomes uniformly dispersed throughout the molten additive. Where more-than one additive is employed, they are preferably, but not necessarily, all rendered molten. The melting point of any additive to be melted in forming any 10 of the blends of this invention should, of course, be below t.le decomposition temperature of any other material wi~h which it is to be melt blended. It should not be so low, however, that the particles of blended materials become tac~y near temperatures at which they would be stored or trans-15 ported. Preferably, the additives are chosen such that theyand their mixtures with one another and with the indicator substance will melt above about 40~C.
Following the melt blending step, the melt is converted to solid particulate form. Preferably, the solid particles 20 have a mesh size smaller than 20 U.S. mesh when added to the polymer. Most preferably, the particle size is between 80 and 20 U.S. mesh (180 to 840 microns diameter). If the particular method by which the blend is formed does not result in such a product, this can be accomp]ished by conventional 25 means, such as gLinding, ball milling, spray chilling or extruding into strands which are then cu-t into pellets.
Methods which l-esul~ in a more or less spherically shaped 11~ 4~
- 8 - 650-6~1 particle are preferred.
Where one or more of the components remains in solid form during the melt blending step, it is desirable that the temperature of the melt be fairly close to its freezing point 5 when blending is terMinated and the melt is allowed to solidify, as is done where grinding or ball milling is to be employed to form the particles of blended material. Preferably, the melt will have taken on a somewhat viscous character before the mlxing is discontinued, in order to prevent any 10 significant degree of settling of any component before solidification of the blended mixture takes place. In general, the temperature of the molten mixture when blending is terminated should be high enough so that it can be poured from the vessel in which it has been blended, yet lcw 15 enough so that its viscosity will inhibit settling of any solid particles, i.e. from about 5 to about 20C. above its ` freezing point.
In melt blending the additive and indicator substance, it is not critical whether the components are in solid or 20 molten form when they are first brought together. The components may be dry-blended before any of them is melted.
The additive~indicator blends may also be produced by dissolving one or more of the components in a solvent and removing the solvent by evaporation after thorough mixing of 25 the dissolved components and any undissolved component, which latter should not exceed one in number. The particular solvent 1~3'~
_ ~ _ 650-6~18 or mixture of solvents used is not cr:itical. Depending on the additive and indicator employed, selection of a solvent is routine, particularly since most product literature specifies suitable solvents.
~here melt blending is used, this may be facilitated by addition of relatively small quantities of a solvent, which may act as a plasticizer and heat-transfer medium. Such a solvent should have a boiling point su~ficiently high that it will remain liquid during at least the early part of the melt blending process, but low enough to enable it to be removed subsequently by evaporation, optionally under vacuum.
The preferred additive-indicator blends are cohesive blends in which the indicator substance is a compound useful as an optical brightener having the above-specified absorption, fluorescence and log fluorescence intensity.
Accordingly, the invention further provides a uniform cohesive blend (as hereinbefore defined)comprising an additive capable of improving the properties of a thermoplastic organic polymer and a fluorescent optical brightener.
The polymers in which the a~ove-descrihed blends may be incorporated include any thermoplastic organic polymer which can be processed at temperatures below tlle decomposition temperatuxes of any blend components, for example polyamides, polyurethanes, polyacrylates, ABS copolymers and, particularly, polystyrenes, polycarbonates, polyvinyl chloride, polyesters (e.g., polyethylene texephthalate~, and synthetic rubberf mosi

4~
- 10 ~ ~50-681~

especia]ly polyol~fins of both lligh anc1 low density, such as polyetllylene and polypropylene and their copolymers.
The additive-indicator blend may be incorporated in the polymer in the same manner in whic:h additives are usually added to thermoplastic polymers. Preferably, the solid particulate blend and the polymer, also in solid particulate form, are dry blended and then r~ndered molten, melt blended and shaped, preferably by being extruded and cut into pe]lets.
The amount of blend employed ~7i] 1 be that amount necessary to give the concentration o~ additive i,n the polymer which would normally be used if the aaditive were being added in its conventional form. That amount will, of course, depend on whether it is desired to achieve the final concentration immediately or to produce an additive-polymer concentrate which can be diluted later with more polymer, i.e. a master-batch.
Because of the uniform and preferably cohesive character of the additive-indicator blend ~hen it is added to the polymer, the presence of indicator in a sample portion of the processed polymer assures the essentially identical distribution of additive in that portion. While some small clegree of separatlon of the additive and lndicator substance may occur in the molten polymer, this is not sufficient ~o detract from the reliability of the method. By knowing the propor-tion of indicatoL in the blend, the proportion of additive in the sampl2 can be immediately ii3~4 ~ 650 6~1 determined. For example, if 0.2 grams of indicator are blended with 99.8 grams of addit:ive, the presence of indicator in a sample assures the presence also of addi-tive in an amount ~99 times that of the indicator. Thus, even by a simple visual inspection under ultraviolet light of a sample portion from a polymer batch to which the blend has been added, i~ can be determined frorn the presence or absence of fluorescence or from the intensity of the fluorescence whether the additive was distributed into that portion of the polymer batch and the relative proportion thereof.
The availability of a wide range of fluorescence spectrophotometers makes quantitative measurements possible.
Such instruments as the Hunter Reflectometer Moclel D25 and the Farrand Fluorometer Model A~ are suitable examples.
The fluorescence intensity or degree of whiteness of a polymer sample will vary directly with the concentration of fluorescent compound which it contains. For each comb-ination of a particular polymer and a particular additive-indicator blend, a standard calibration curve can be 20 established which gives the instrument readings, i.e.
fluorescence intensity or whiteness degrees, for a series of different concentrations of the blend in the polymer. During a subsequent production run using the same polymer and blend in a particular proportion, the operator ta~es a reading on a 25 portion of the polymer-blend mixture at some staq2 of its processing and con.pares that reading with the value on the `` 1~3~

~.2 - 650-6~18 calibration CU]^Ve for that particu]ar concentration. If the reading is too higll or too low, :it indicates that an ex-excessive or insufficient amount of indicator and hence a coîrespondingly excessive or insufficient amount of additive is present in the portion tested, and appropriate adjust-ments can be n^~ade in the feed rates or in the blending operation to eith2r adjust the propQrtions of polymer and additive-indicator blend or to effect more uniform distrib-ution. Using a different type of irradiation-responsive indicator substance and an appropriate measuring apparatus, similar results can be achieved.
The analysis may be carried out at various stages of processing. Primarily, it is intended that the product extruded or molded from the polymeric material will be analyzed to determine the uniformity of distribution of the indicator and additive in the product. As a preliminary check, the dry-blended mixture of polymer and additive-indic-ator particles rnay be tested to determine the uniformity of the distribution ofindicator-containing particles throughout 20 the mixture. As a still further check, the additive-indicator blend may be tested to ascertain the uniformity of distrib-ution of the indicator throughout the additive. Depending on the number of mixing stages in the overall process, additional analysic~ can be c~arried out. Moreover, the appropriate 25 instrumentation can be included as part o the processing equipment to provide for continuous or intermittent on~line ' 113~
- 13 - 650 6~1 inspection, so that adjustments ln feed rates and blending can be made pron~tly when needed.
Preferred concentrations of the optical brightener in the cohesive blend of additive and brightener are from 2% to 0.001Sor more preferably 0. l~o to 0~005So by ~eight.
The following examples illustrate the invention.
Parts and percentages are by weight, and tempe~atures are in degrees centigrade, unless othert~Jise specified.

.

' ~3~4 - 14 - ~50--6~18 EXAMPLE. 1 A
In a vessel equipped with a stirrer, 49 parts of a stabilizer of the formula I, C(CH3)3 C(CH3)3 [( 3)3 C4~0; P CO~\~P-~O~(CII3)~1 I

are heated to melting (m~p. 82-87). To this are added with stirring 49 parts of an anti oxidant of the formula II, O C ( CH3 ) 3 - . .
C- - CH2-O-C-c~I2cH2 ~ ~ OH II

C(CH3)3 and heating is increased until the second compound melts (m.p. 117-125C.). To the molten mix'.ure is added 2 parts of an optical brightnener of the formula III

~ N ~ ~ ~ III

and vigorous stirring is continued until the brightener is homogeneously disp~rsed therein ~approximately 45 minutes~.
With the temperature at about 85, stirr1ng is discontinued ~3~4 - 15 - 650-681~

and the molten blend is immediately poured into a shallow pan and allowed to solidify at room temperature. The resulting solid block is ball milled to a particle size in the range 80 to 20 mesh.

In a c]osed cylindrical vessel on a two roll mill 5 parts of the solid particulate blend prepared according to Part A and 95 parts of low density polyet.~ylene powder are mixed for 30 minutes. This solid mixture is then heated to 120 in the same container on a heated two roll mill for 12 hours, so that the blend is thoroucJhly dispersed in the molten polymer. This concentrate contai~ing 0.1% brightener, 2.45~ stabilizer and 2.45% anti-oxidant is then allowed to solidify and is ground to a powder.
Various quantities of this concentrate powder are then further diluted and blended with 100 part portions of low density polyethylene to produce sample mixtures containiny 1, 5, 10, 20, 50,and 100 ppm brightener and the proportionate amounts of stabilizer and anti-oxidant. Each of the sample mixtures is pressed at lC-under 20,000 psi to form a film. Each film is tested with a E~unter Reflectometer Model D25 to measure whiteness, ~7ith the following results:

.

~3~ 4 - 16 - 650-6~18 . _ Brightener ppm Concentration 1 5 10 20 50 100 .. _.____ _ . ._ ~
~w 6 17.5 25.5 32.842.5 46 Five parts of the stabilizer-brightener blend prepared in Step R and 19995 parts of the low density polyethylene powder are thoroughly mixed in a ribbon blender. Based on its total weight, the resulting mixture contains 5 ppm brightener. To determine whether the brightener and, there-fore, the stabilizers with which it has been blended are uniformly distributed throughout the polymer powder, a sample thereof is tested with the ~unter Reflectometer.
A ~ ~w of 17.5 indicates that the proper degree of distribution has been achieved.
The uniform blend of polymer, additives and briyhteners is then passed to a melt extruder for formation into ribbons or pellets. A portion of the extruded product is analyzed with the Reflectometer and a reading of 17.5 again indicates that the tested portion contains the desired amount of indicator and, therefore, also contains the desired 0.0122 of each additive.

The procedure of Step A of Lxample 1 is repeated, except that the optical brightener is added prior to the anti-oxidant. This sequence provides more efficient dispersal of the optical brightener throughout the molten blend of additives.

. _ _ The procedure of Example 1 is repeated using poly-propylene in place of the low density polyethylene, with similar results.

Step A of Example 1 is repeated except that the anti-oxidant is of the formula IV

~ C (CEi3 ) 3 - C18H37-O-c CH2CH2~~ OEI IV

C (CH3) 3 The resultin~ product is suitable for incorporation into various thermoplastic organic polymers in accordance with the present invention.

E~XAMPLE 5 The procedure of Example 1, Step A is repeated except that, upon adding the optical brightener,the temperature is raised to about 175, whereupon the brightener becomes homogeneously admixed with the stabilizer and anti-oxidant.
The temperature is then lowered to about 125 and ~he molten mixture is spray chilled to form substantially spherical 113~ 4 particles.

A mixture of 35 parts of the stabilizer of formula I, 35 parts of the anti-oxidant of formu]a II, 17.5 parts calcium stearate, 17.5 parts zinc stearate and 0.02 parts of the optical brightener of formula III are melt blended by stirring at 150 under a nitrogen atmosphere. The melt is poured into a shallow tray, cooled and ground, giving particles of m.p. 92-93.

A mixture of 166.6 parts of the stabilizer of formula I, 83.3 parts calcium stearate, 83.3 parts zinc stearate and 0.05 parts of the optical brightener of formula III is stirred with a solution of 166.6 parts of the anti-oxidant of formula II in 334.1 parts of chloro~enzene under a nitrogen atmosphere at 160. The chlorobenzene evaporates first under normal pressure and finally with the aid of a water-pump vacuum. The residual melt is poured into a shallow tray, cooled and ground, giving particles of m.p. 91-93; containing 100 ppm optical brightener.

To 100 part portions of high density polyethylene ~ (~) powder (Manol~ne ~ype ~095) is added 0.25, 0.5, 0.75 or 1 part of the cohesive blend prepared in Example 7. The .

1136~344 components were mi.xed by sha]~ing together in a plastic bay, then extruded in a laboratory extruder at 120 rpm and a temperature profile of 120/210/220/200. The relative fluorescence intensity (FI) of the resulting granulate was measured against a whiteness standard in a Perkin Elmer MPF 4 fluorescence-spectrophotometer.
The following table gives the relative FI values of two independent extrusion experiments, and shows the good repxoducibility of the method. If the relative fluorescence intensity is plotteZ. against the concentration of the blend, all values lle approximately on a straight line.

. _ . _~ _ parts cohesive blend Concentration of relative F.I.
of Ex. 7 per 1000 optical brightener, parts polymer ppm . _ _ _ _ _ . ~ _ . .... I

0.25 0.025 1.7 1.8 0.5 0.05 3.3 3.3 0.75 0.075 4.7 4.6 1.0 0.10 5.9 6.1 . . .. ~_ ~ .

_ _ The following examples indicate further comb1n2tio~s of-additives and optical brighteners .suitable for the formation of cohesive blends according to the precent invention.

~ ' ' - ~ ' ~ -, , ' ' . ' ~

1~3~
- 2 1 6 5 0~

~__ ~ _ _ ~
E clm~].e Componen t . unciti.on ( ~
__~ ~_~ ~ .~_~ . - .~

l .~ C 1 2 ~: ~ 5 C I A 2 C, . C i 2 2 2 antistatic G0 60. 0 . acJen '-II an t ic~:idant 2 0 2 0 . 0 I st2bilizer 19 19 . 99 III bri~htener l 0 . 01 . _. _ . ,___ _ . ._ 14 fat~ y acid am~e slip ac3ent 95 95 . 0 C ( CY 3 ) 3 ant io~ .id ant 4 4 . 9 9 III bric~htcner 1. O 0 01 . . ~ . . . .. .. . . .. ._. . ... ~

~3L3~ 4 20 - 650-6Zl~

E amy1e ~ Component ~ ctio~ (a~
_ ._. .~ .. . ~ ~
9 II antio~idant¦ 99.5 99~99 ¦
III bri~lltenex0.5 0.01.¦
.. _~ . _ ~-1 R antio~idant 4g.5 50.0 i CH3 ~ 3 CH3 t-bu~71 where ~ 2 ~ OI~
t-butyl . stabilizer 49.5 49.9g III brightener i.0 O.Ql ~ _ _ .. . ~.
11 II antioxidant 33 33.33 distear.yl-thio-di- anti.o,;idant 33 33~33 ~xoprionate . st~bilizer 33 33.33 III brlghten~r 1 0.01 12 ~ ~ ~ -O nC~17 UV absorber 83 83.50 I stabilizer 16 16 . 4~7 _ ~ ~ C(CH3~ ) .

. .

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the production of a thermoplastic organic polymer containing an additive selected from the group consisting of anti-oxidants, heat-stabilizers, UV-stabilizers, lubricants, flame proofing agents, slip agents, anti-blocking agents and anti-static agents, comprising the steps of incorporating into the thermoplastic organic polymer a composition comprising a uniform blend of the additive and an indicator substance compatible with the additive and the thermoplastic polymer, stable under the processing conditions to which it will be subjected, and which gives a detectable response to irradiation in the presence of the additive, subjecting at least part of the product to the irradiation to which said indicator sub-stance is responsive and determining from the degree of response the amount of the additive in that part of the product.

2. A process as claimed in Claim 1 in which the indicator substance is a fluorescent substance which absorbs ultraviolet light in the range 300 to 420 nm and fluoresces in the range 400 to 700 nm.

3. A process as claimed in Claim 2 in which the fluorescent substance has a log fluorescence intensity equal to or greater than 3 at room temperature and at a concentration of 1 part per million in a solvent mixture of diethylether, isopentane, ethanol and chloroform in a volume ratio of 75:75:30:20.

4. A process as claimed in Claim 3 in which the fluorescent substance is an optical brightener.

5. A process as claimed in Claim 1 in which the uniform blend of the additive and the indicator substance is a cohesive blend, that is, in the form of solid parti-cles, of which each particle comprises a mixture of additive and indicator substance, the distribution of the additive and the indicator substance in the cohesive blend being uniform.

6. A process as claimed in Claim 5 in which the cohesive blend is prepared by melt blending and converting the molten mass to a particulate solid.

7. A process as claimed in Claim 1 in which the thermoplastic polymer is a polyolefin.

8. A process as claimed in Claim 1 in which the mixing of the thermoplastic polymer with the uniform blend of additive and indicator is a continuous process, and in which the mixing conditions are regulated on the basis of a continuous or intermittent determination of the response to irradiation of the indicator substance in the product.

9. A process as claimed in Claim 8 in which the continuous mixing process is carried out in an extruder.

10. A process as claimed in Claim 1 in which the concentration of indicator substance in the product polymer is from 0.001 to 100 ppm.

11. A process as claimed in Claim 10 in which the concentration is from 0.05 to 5 ppm.

12. A uniform cohesive blend, defined in Claim 5 comprising a fluorescent optical brightener and an additive selected from the group consisting of anti-oxidants, heat-stabilizers, W-stabilizers, lubricants, flame proofing agents, slip agents, anti-blocking agents and anti-static agents.

13. A cohesive blend as claimed in Claim 12 containing from 2 % to 0.001 % by weight of the optical brightener.

14. A cohesive blend as claimed in Claim 13 containing from 0.1 % to 0.005 % by weight of the optical brightener.

15. A cohesive blend as claimed in Claim 12, 13 or 14 in which the optical brightener is of formula III

III

16. A cohesive blend as claimed in Claim 12, 13 or 14 in which the additive comprises at least one of a stabilizer of formula I

an anti-oxidant of formula II

II

and an optical brightener of formula III

III

17. A process for the production of thermoplastic organic polymer containing an additive selected from the group consisting of anti-oxidants, heat-stabilizers, UV-stabilizers, lubricants, flame proofing agents, slip agents, anti-blocking agents and anti-static agents and a fluorescent optical brightener comprising the step of incorporating into the polymer a cohesive blend of additive and optical brightener as claimed in Claim 12.